1. Field of the Invention
This invention relates to packet switched telecommunications systems and, more particularly, to a method and system for controlling packet switched radio channel congestion in a telecommunications system.
2. History of the Prior Art
As the capability to offer a greater number and variety of services within cellular telecommunications systems develops, packet switched services will play an increasingly important role in the field of cellular telecommunications. The application of many computer and related data services to cellular systems requires the transfer of single or multiple data packets over the radio link of a cellular telecommunications system. Certain of these services such as e-mail and tele-banking may be implemented with a store and forward short message service. Other services, such as terminal emulation, local area networks, bank server access, and credit card verification, however, require interactive usage, short time delays and the capability to handle data packets of widely varying lengths. It is certain that future cellular systems will have to support such services with an efficient packet-data service.
Recognition of the importance of packet data services has resulted in the current effort of the European Technical Standards Institute (ETSI) to develop such a service for the European 2+ Group Special Mobile (GSM) cellular system. This recognition has also resulted in an effort to design packet-data service capability into the Universal Mobile Telephone System (UMTS) currently under development in the RACE II Code Division Testbed (CODIT) project R2020. The CODIT project was set up by the Commission of the European Community for the purpose of defining a future mobile telecommunications system using code division multiple access (CDMA) techniques.
Packet-switched data service in a cellular telecommunications network is characterized by calls from network users to mobile users being transmitted to packet switched mobile stations on the shared downlink (DL) of a packet switched radio channel (PRCH) and, by one or more mobile users sharing the uplink (UL) of the PRCH. The DL PRCH is shared by network users on a queued basis. The UL PRCH is shared by each mobile user accessing the channel in random fashion, as the mobile user requires, to transmit data to the system.
A common method of allowing access to the PRCH is through a packet-switched contention mode. The currently defined CODIT UMTS packet-data service is of the contention mode type. In the packet-switched contention mode mobile users transmit data packets on the PRCH when it is necessary to transfer data. An identification of the transmitting mobile user is contained in each data packet. The transmission of data packets by the mobile user may be done either randomly, or upon sensing an idle signal indicating that the packet-data channel is not presently used by another mobile station. If two or more mobile users simultaneously contend for an idle packet-data channel, the system will only allow one access to the channel. Mobile users unsuccessful at accessing the channel must repeat the transmission of the data packet until it is accepted by the system. The system users transmitting data packets to mobile users also contend for the downlink by being placed in a queue.
Because in such a system each user accesses the packet-switched channel in a random fashion, uncontrolled flow of users to, from, and between the packet-switched radio channels of a cellular system may cause packet transmission delays in the system. The delay may be incurred by both mobile users on the uplink and network users transmitting to mobile users on the downlink. As the number of packet calls on the packet switched channel increases, the average transmission delay for each packet call increases. In some applications the delays may be unacceptable.
Therefore, a need exists for a method and system for controlling packet transmission delay on one or more packet switched radio channels of a cellular system. If contending packet calls could be selectively chosen for admission to a packet radio channel according to predefined criteria, delays for packet switched channel users in applications that cannot tolerate a long packet delay time could be avoided and reduced.
A method and system for managing the flow of prioritized users to, from, and between one or more packet switched radio channels, with each packet switched radio channel having a maximum tolerable packet transmission delay, would meet such a need.